Historically the use of precured treads was limited to retreaded tires exclusively. Tire casings are designed to survive several times longer than the tread. This is particularly true of truck tires and low aspect ratio passenger tires.
The Goodyear Tire & Rubber Company in the late 1980's introduced the Unicircle precured injection molded tread. This precured tread is disclosed in European Patent Publication 0-464-660A1. This annular or acutely shaped tread had short annular wings radially inwardly extending. The wings were flexible and adapted to accommodate casings of various axial widths. This tread introduced high-pressure injection molded rubber compounds having excellent wear and rolling resistance properties. Materials used in tread rubber compounds have also been improved making it feasible to transfer compression mold high quality treads for tires which can also achieve excellent wear and performance characteristics.
Later development efforts were concentrated on improved adhesion of the tread to the casing and in particular at better ways of adhering the wing edge to the casing. On May 24, 1994, U.S. Pat. No. 5,313,745 issued to Carl L. Mace, Jr., et al. relating to a tread edge grinning method which effectively created a chamfered edge enabling the cushion gum rubber to migrate over the chamfer effectively locking the annular wing of the precured tread to the cushion gum and the casing.
The advancement in the overall adhesion properties of the tread to casing bond coupled with the ability to meet or surpass the performance of conventional molded new tires means that it is now feasible for new tires to be made using precured treads. One aspect of the present invention describes an improved precured tread and a method for assembling it to a previously unvulcanized casing. A second aspect of the invention teaches how the tread can be applied to a precured new casing or a used prepared vulcanized casing. In each case, the invention permits the adhesion of the tread at the sidewall to exceed that achieved in the Mace patent while at the same time creating an almost imperceptible seam line between the casing and the tread.
A common concern in the tire art relates to the uniformity of tire construction and therefor tire performance. The inventors believe that once cause of poor and inconsistent tire performance relates to the non-uniform pressure distribution exerted on tire casings during the tire curing process. In particular, the inventors believe that belts can be distorted due to the non-uniform pressure exerted by the mold in the tread groove area. The present invention overcomes this problem by providing uniform pressure distribution on the casing during curing. Thus, tire life and performance is enhanced.